This study investigates the potential and educational values of cross-boundary learning in music appreciation activities at junior high school music education. Boundary crossing refers to actions that transcend the boundaries with communities in the field of practice. By examining music appreciation classes from the perspective of boundary crossing, the authors derive suggestions for issues currently facing educational practitioners in the field. The authors implemented an activity for second graders of X Junior High School, in which they presented a song of their choice to one another. The authors analyzed the music selected, the students' narratives during the activity, and their reflections. The results revealed that the practice functioned as a site of hybridization, allowing students to cross-boundary between the school music education and everyday life, between self and others, and generating horizontal and vertical learning.